Arlington's new, non-metallic enclosure boxes are the perfect solution to protecting and securing power backups, security devices and other valuable equipment indoors oor outside. Made of heavy-duty, UV rated non-metallic material, and available in three sizes, our boxes are NEMA 3R rated for outdoor use when mounted with the hinge on top. Outdoor rated non-metallic enclosures, NEMA3R. Gray, 11 x 11 x 3.5. Using a back plate allows an installer to mount components to the plate even after the enclosure box is mounted. Changing batteries and doing other maintenance work is easily accomplished by removing the plate. Arlington’s enclosure boxes are ‘lockable’ via a knockout on the front of the box for a cam lock – or a latch that holds a padlock.